(of a chemical spray or other substance) not able to be washed away by rain.
Example sentencesExamples
- This spray is longer lasting than the copper sprays used on tomatoes, and it is rainfast.
- Allow at least six hours for the glyphosate products to become rainfast.
- This product is cheaper, has a better safety profile, controls both types of rhizomes and is rainfast after 2 hours.